W W W . G O L D E N A G E P R O J E C T . C O M
II
CIRCUIT DESCRIPTION
The signal first enters an input transformer.
The primary of the input transformer has
two windings that are either connected in
series or in parallell which results in an
input impedance of either 1200 Ohm or 300
Ohm (in MIC mode).
The transformer are followed by two input
gain stages. For gains up to 40 dB, only one
of them is being used. For gains from 45 dB,
the second gain stage is inserted in the signal path. Both gain stages uses
only three transistors each.
The signal then goes to the Insert connector with its bypass jumper, to the
Output level potentiometer and from there on to the output stage. This stage
again only uses three transistors, the last one in the chain is a hefty 2N3055
power transistor run in class-A mode, driving the output transformer.
So, all in all, the complete signal chain only contains a maximum of nine
active elements. Compare that to the big number of transistors that are usu-
ally used in one single integrated circuit!
USING THE PRE-573 MKII
Using a preamplifier is not rocket science. Here are some points though to
help you getting the maximum out of the PRE-573 MKII:
- As a start, you need to mount the module in a 500 series rack unit. There
are several alternatives available from different manufacturers, the PRE-573
MKII should work fine in most of them. Make sure that the rack unit power
supply is turned off when you mount or remove the PRE-573 MKII.
MIC / LINE INPUT
Connect your Mic or Line source to the input connector on the 500 rack unit
corresponding to the slot where the PRE-573 MKII is placed.
For Microphone sources:
1. Set the MIC - LINE switch to the MIC position.
2. Set the MIC/LINE - ACTIVE DI switch to the MIC/LINE position.
3. Set the PASSIVE DI switch to the downward off position.
4. Engage the +48 V if the connected mic needs phantom power. It is good
procedure to always disengage the phantom power and wait for about 10
seconds before unplugging a mic.
- The 300 - 1200 switch will select the input impedance. 1200 ohm is the
normal position for most mics. Lowering the mic input impdance to 300
ohm will change the tone of many microphones and will give you one more
soundshaping option.
For Line level sources:
1. Set the MIC - LINE switch to the LINE position.
2. Set the MIC/LINE - ACTIVE DI switch to the MIC/LINE position.
3. Set the PASSIVE DI switch to the downward off position.
The LINE input mode will attenuate the input signal with about 30 dB and
also increase the input impedance to about 10 kohm.
- If you want the smallest amount of coloration, always set the OUTPUT level
potentiometer at or close to maximum, and adjust the output level with the
stepped GAIN switch.
The +10 - 0 - +5 dB switch should normally be in the 0 position but you can
set it to +5 or +10 dB anytime you want to add gain.
The +5 and +10 dB positions of this switch corresponds to the -75 and -80
dB positions (with the PRE-573 MKII GAIN switch set to 70 dB) and the -45
and -50 dB positions (with the PRE-573 MKII GAIN switch set to 40 dB ) in the
classical 1073 unit.
- If you want more character, turn the OUTPUT level potentiometer counter-
clockwise and increase the gain with the GAIN switch. This will drive the
input gain stage(s) harder and provoke more character from them.
DI INSTRUMENT INPUT
Instruments that are not connected to the mains AC power line can be con-
nected to the DI instrument TRS input on the front panel.
The DI input has two selectable modes, Passive and Active. The Active mode
uses a FET-buffer and has an input impedance of about 1,5 Mohm. The
signal is fed through the input transformer and then onwards to the gain
stage(s).
The Passive mode feeds the signal from the TRS jack directly to the gain
stage(s). It has an input impedance of about 100 kohm.
To use the Active mode:
1. Set the MIC/LINE - ACTIVE DI switch to the ACTIVE DI position.
2. Set the PASSIVE DI switch to the off position, ie, the downward position.
To use the Passive mode:
Set the PASSIVE DI switch to the On position, ie, the upward position.
Please note:
- DO NOT use a higher GAIN than 70 dB in Passive mode and 50 dB in the
Active mode (you can try it if needed but self oscillation might occur).
- The DI input in Active mode has a much higher sensitivity than the Passive
mode so GAIN must be set lower than in the Passive mode for the same
output level. The input impedance is also much higher so the DI input will
load the connected instrument less compared to the Passive mode.
- The tone of most instrument will differ in the two modes giving you several
sound options.
- Some instruments will sound and work better in one of these modes, the
best way of finding out is to experiment.
- Signal sources connected to the 500 rack input can remain connected
when you use the DI input.
- DO NOT connect mains connected equipment to the DI input (unless they
have a fully floating, transformer balanced output), then use normal MIC/
LINE input on the 500-rack.
OTHER FUNCTIONS
The 3 position AIR - OFF - PHASE switch works like this:
1. The Phase position simply reverses the phase by reversing the wires from
the secondary winding of the output transformer. Reversing the phase of the
signal is useful on a number of occasions, one example is phase reversing
the the lower mic on a snare drum to make it sum in phase with the upper
mic.
2. In the middle position of the switch, the phase is not reversed.
3. Putting the switch in the upper AIR position
adds a boost of about 6 dB
centered at about 30 Khz. It will affect the range from about 5 kHz and up.
There is an unbalanced Insert connector located at the back of the unit
where you can insert Golden Age Project 500 Series effect modules. The
operating level is about -18 dBu. To activate the insert, the jumper located
close to the connector must be removed.
The output transformer used in the PRE-573 MKII is designed for having
an ideal load of about 600 ohm. The input impedance of most modern units
is 10 kohm or more. The PRE-573 MKII has a jumper selectable 600 ohm
output termination resistor. The jumper, which is located at the back of the
unit, is connected from factory to set the load to the ideal 600 ohm when
modern units are connected after the PRE-573 MKII. This will lower the high
end frequency response slightly which can sometimes be a good thing.
Disengaging the termination resistor by removing the TERM jumper will
result in a slightly higher level in the upper frequency range (mainly above
20 kHz) when modern units are connected after the PRE-573 MKII.
The termination jumper option, together with the AIR option, makes it pos-
sible to achieve different high frequency response curves.
WARRANTY
The PRE-573 MKII is built to last. But as in any electronic device, compo-
nents can break down. If the unit has a problem and will need repair, you
should contact the reseller where you bought the unit.
The warranty period is decided by the Distributor for your country. The
Distributor will support Golden Age Project resellers and end users with
repairs and spare parts.
REGISTRATION
You are welcome to register your unit at: www.goldenageproject.com
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I would like to thank you for chosing the PRE-573 MKII!
I hope it will serve you well and that it will help you in making
many great sounding recordings.
Yours, Bo Medin
Vintage character
for modern ideas!
